Typescript類型體操 - IsNever

題目

中文

實現一個以 T 作爲泛型參數的 IsNever類型.
如果 T 是never, 返回 true, 否則返回 false.

示例:

type A = IsNever<never>; // expected to be true
type B = IsNever<undefined>; // expected to be false
type C = IsNever<null>; // expected to be false
type D = IsNever<[]>; // expected to be false
type E = IsNever<number>; // expected to be false

English

Implement a type IsNever, which takes input type T.
If the type of resolves to never, return true, otherwise false.

For example:

type A = IsNever<never>; // expected to be true
type B = IsNever<undefined>; // expected to be false
type C = IsNever<null>; // expected to be false
type D = IsNever<[]>; // expected to be false
type E = IsNever<number>; // expected to be false

答案

type IsNever<T extends unknown> = [T] extends [never] ? true : false;

在線演示